A function to encode text as a QR code using BitmapPainter and zxing-core for use in jetpack compose with Image composable.

QRPainter.kt

@Composable
fun rememberQrBitmapPainter(
    content: String,
    size: Dp = 150.dp,
    padding: Dp = 0.dp
): BitmapPainter {

    val density = LocalDensity.current
    val sizePx = with(density) { size.roundToPx() }
    val paddingPx = with(density) { padding.roundToPx() }


    var bitmap by remember(content) {
        mutableStateOf<Bitmap?>(null)
    }

    LaunchedEffect(bitmap) {
        if (bitmap != null) return@LaunchedEffect

        launch(Dispatchers.IO) {
            val qrCodeWriter = QRCodeWriter()

            val encodeHints = mutableMapOf<EncodeHintType, Any?>()
                .apply {
                    this[EncodeHintType.MARGIN] = paddingPx
                }

            val bitmapMatrix = try {
                qrCodeWriter.encode(
                    content, BarcodeFormat.QR_CODE,
                    sizePx, sizePx, encodeHints
                )
            } catch (ex: WriterException) {
                null
            }

            val matrixWidth = bitmapMatrix?.width ?: sizePx
            val matrixHeight = bitmapMatrix?.height ?: sizePx

            val newBitmap = Bitmap.createBitmap(
                bitmapMatrix?.width ?: sizePx,
                bitmapMatrix?.height ?: sizePx,
                Bitmap.Config.ARGB_8888,
            )

            for (x in 0 until matrixWidth) {
                for (y in 0 until matrixHeight) {
                    val shouldColorPixel = bitmapMatrix?.get(x, y) ?: false
                    val pixelColor = if (shouldColorPixel) Color.BLACK else Color.WHITE

                    newBitmap.setPixel(x, y, pixelColor)
                }
            }

            bitmap = newBitmap
        }
    }

    return remember(bitmap) {
        val currentBitmap = bitmap ?: Bitmap.createBitmap(
            sizePx, sizePx,
            Bitmap.Config.ARGB_8888,
        ).apply { eraseColor(Color.TRANSPARENT) }

        BitmapPainter(currentBitmap.asImageBitmap())
    }
}

Hi, I wanted to start by saying thank you for sharing this QR code generation code. It's clear that a lot of effort and expertise went into it, and it's been very helpful. I've been using it in a LazyColumn and noticed some performance issues. After some investigation, I found that the bitmap generation could be optimized. Instead of setting pixels on the bitmap one at a time using setPixel, which can be quite slow, you could create an array of the pixel values and then use setPixels to set all the pixels at once. This change significantly improved the performance in my case. Here's the modified part of the code for your reference:

val pixels = IntArray(matrixWidth * matrixHeight)

for (x in 0 until matrixWidth) {
    for (y in 0 until matrixHeight) {
        val shouldColorPixel = bitmapMatrix?.get(x, y) ?: false
        val pixelColor = if (shouldColorPixel) Color.BLACK else Color.WHITE

        pixels[y * matrixWidth + x] = pixelColor
    }
}

newBitmap.setPixels(pixels, 0, matrixWidth, 0, 0, matrixWidth, matrixHeight)

I hope this suggestion might be useful to you or others who are using your code. Thanks again for your great work!

Thanks for this gist! I forked to provide an Image Composable with circular indicator while the QR code renders.
It also includes the import statements and the performance enhancement from @SherifMuSherif.

https://gist.github.com/ryanholden8/6e921a4dc2a40bd40b3b5a15aaff4705